{"id":1820,"date":"2021-04-15T20:27:06","date_gmt":"2021-04-15T12:27:06","guid":{"rendered":"http:\/\/47.101.202.111\/?p=1820"},"modified":"2023-04-07T16:29:46","modified_gmt":"2023-04-07T08:29:46","slug":"algorithm-tree-array","status":"publish","type":"post","link":"http:\/\/139.196.114.170\/?p=1820","title":{"rendered":"\u524d\u7f00\u95ee\u9898\u9ad8\u6548\u89e3\u6cd5 &#8211; \u6811\u72b6\u6570\u7ec4\u8be6\u6089"},"content":{"rendered":"<h2>\u7efc\u8ff0<\/h2>\n<p>\u6811\u72b6\u6570\u7ec4\u662f\u89e3\u51b3 <strong>\u524d\u7f00<\/strong> \u76f8\u5173\u95ee\u9898\u7684\u4e00\u79cd\u6570\u636e\u7ed3\u6784<br \/>\n\u5728\u524d\u7f00\u76f8\u5173\u95ee\u9898\u4e2d\u53ef\u5229\u7528\u524d\u5e8f\u5df2\u8ba1\u7b97\u7ed3\u679c\u907f\u514d\u91cd\u590d\u8ba1\u7b97\u964d\u4f4e\u590d\u6742\u5ea6<br \/>\n\u65f6\u95f4\u590d\u6742\u5ea6 <code>$$\\scriptsize O(log_2n)$$<\/code>\uff0c\u53ef\u5bf9\u76f8\u5173\u95ee\u9898\u8fdb\u884c\u7b97\u6cd5\u4f18\u5316<\/p>\n<h2>\u601d\u60f3<\/h2>\n<p>\u5bf9\u4e8e \u6811\u72b6\u6570\u7ec4 <code>$$\\scriptsize bit[N]$$<\/code> \u548c \u6570\u636e\u6570\u7ec4 <code>$$\\scriptsize a[N]$$<\/code><br \/>\n\u6811\u72b6\u6570\u7ec4\u7684\u6bcf\u4e2a\u8282\u70b9\u8868\u793a <strong>\u6570\u636e\u6570\u7ec4\u4e00\u4e2a\u533a\u95f4\u5185\u6240\u6709\u8282\u70b9\u7684\u5408\u8ba1\u4fe1\u606f<\/strong>\uff0c\u5982\u533a\u95f4\u548c\u3001\u533a\u95f4\u79ef\u7b49\uff0c\u5176\u533a\u95f4\u957f\u5ea6\u4e3a <code>$$\\scriptsize lowbit(x)$$<\/code>\u3002\u5373 <code>$$\\scriptsize bit[x]$$<\/code> \u8868\u793a <code>$$\\scriptsize a(x- lowbit(x), x]$$<\/code> \u533a\u95f4\u4e2d\u7684\u5408\u8ba1\u4fe1\u606f<\/p>\n<pre lang=\"cpp\">\nint lowbit(x) { return x & -x; }\n<\/pre>\n<p>\u5982\uff0c<br \/>\n\u8282\u70b9 <code>$$\\scriptsize bit[3]$$<\/code> \u533a\u95f4\u957f\u5ea6\u4e3a <code>$$\\scriptsize lowbit(3) = 1$$<\/code>\uff0c\u8868\u793a\u8282\u70b9 <code>$$\\scriptsize bit[3] = a[3]$$<\/code><br \/>\n\u8282\u70b9 <code>$$\\scriptsize bit[15]$$<\/code> \u533a\u95f4\u957f\u5ea6\u4e3a <code>$$\\scriptsize lowbit(15) = 1$$<\/code>\uff0c\u8868\u793a\u8282\u70b9 <code>$$\\scriptsize bit[15] = a[15]$$<\/code><br \/>\n\u8282\u70b9 <code>$$\\scriptsize bit[6]$$<\/code> \u533a\u95f4\u957f\u5ea6\u4e3a <code>$$\\scriptsize lowbit(6) = 2$$<\/code>\uff0c\u8868\u793a\u533a\u95f4 <code>$$\\scriptsize a[5,6]$$<\/code> \u7684\u5408\u8ba1\u4fe1\u606f<br \/>\n\u8282\u70b9 <code>$$\\scriptsize bit[16]$$<\/code> \u533a\u95f4\u957f\u5ea6\u4e3a <code>$$\\scriptsize lowbit(16) = 16$$<\/code>\uff0c\u8868\u793a\u533a\u95f4 <code>$$\\scriptsize a[1,16]$$<\/code> \u7684\u5408\u8ba1\u4fe1\u606f<\/p>\n<p>\u7531\u6b64\u5927\u533a\u95f4\u8ba1\u7b97\u53ef\u5206\u89e3\u4e3a\u5c0f\u533a\u95f4\u4fe1\u606f\u7684\u5408\u8ba1\uff0c\u5206\u89e3\u6b65\u9aa4\u5982\u4e0b\uff0c<br \/>\n<code>$$\\scriptsize sum(a[1,i]) = sum(a[1\uff0cj]) + sum(a[j + 1, i]) = bit[i] + bit_{sub}[j],j = i - bit[i]\u533a\u95f4\u957f\u5ea6$$<\/code><br \/>\n<code>$$\\scriptsize sum(a[1,i]) = sum(a[1\uff0ck]) + sum(a[k + 1, j]) = bit[j] + bit_{sub}[k],k = j - bit[j]\u533a\u95f4\u957f\u5ea6$$<\/code><br \/>\n<code>$$\\scriptsize \\cdots$$<\/code><\/p>\n<p>\u5c06\u521d\u59cb\u533a\u95f4\u957f\u5ea6\u4f9d\u6b21\u5206\u89e3\uff0c\u7ed3\u679c\u4e3a <strong>2\u7684\u6700\u5927\u5e42\u6b21\u5206\u89e3(\u5404\u5b50\u533a\u95f4\u957f\u5ea6\u662f\u5927\u533a\u95f4\u4e8c\u8fdb\u5236\u8868\u793a\u7684\u5404\u4f4d\u5341\u8fdb\u5236\u6570)<\/strong>\uff0c\u5982<br \/>\n<code>$$\\scriptsize sum(15) = bit(15) + bit(14) + bit(12) + bit(8) \\\\ = \\sum_{i=15}^{15}a[i] + \\sum_{i=13}^{14} + a[i] \\sum_{i=9}^{12}a[i] + \\sum_{i=1}^{8}a[i] \\\\ = \u957f\u5ea61 + \u957f\u5ea62 + \u957f\u5ea64 + \u957f\u5ea68$$<\/code>\uff0c<br \/>\n<code>$$\\scriptsize sum(8) = bit(8) = \\sum_{i=1}^{8}a[i] = \u957f\u5ea68$$<\/code>\uff0c<br \/>\n<code>$$\\scriptsize sum(6) = bit(6) + bit(4) = \\sum_{i=5}^{6}a[i] + \\sum_{i=1}^{4}a[i] = \u957f\u5ea62 + \u957f\u5ea64$$<\/code>\uff0c<br \/>\n<code>$$\\scriptsize sum(1) = bit(1)= \\sum_{i=1}^{1}a[i] = \u957f\u5ea61$$<\/code><\/p>\n<p>\u5171\u5206\u89e3 <code>$$\\scriptsize O(log_2n)$$<\/code> \u6b21\uff0c\u4e5f\u5373\u8ba1\u7b97 <code>$$\\scriptsize O(log_2n)$$<\/code> \u6b21\uff0c\u6784\u6210\u7531\u521d\u59cb\u533a\u95f4\u4e3a\u7236\u8282\u70b9\uff0c\u5404\u5b50\u533a\u95f4\u4e3a\u5b50\u8282\u70b9\u7684\u591a\u53c9\u6811<\/p>\n<h2>\u5b9e\u73b0\u548c\u5e94\u7528<\/h2>\n<h3>\u524d\u7f00\u548c<\/h3>\n<p>\u5bf9\u4e8e\u4e00\u5217\u5e8f\u5217 <code>$$\\scriptsize a$$<\/code>\uff0c\u6c42 <code>$$\\scriptsize suffix(m,n) = a[m] + a[m+1] + \\dots + a[m+n]$$<\/code>\uff0c\u5176\u4e2d<code>$$\\scriptsize suffix(m,n)$$<\/code> \u662f\u4e3a\u4ee5 <code>$$\\scriptsize a[m]$$<\/code> \u4e3a\u9996\u7684 <strong>\u524d\u7f00\u548c<\/strong><\/p>\n<p>\u8ba1\u7b97\u524d\u7f00\u548c\u7684\u4e09\u79cd\u65b9\u6848<br \/>\n\u2460 \u6bcf\u6b21\u67e5\u8be2\u90fd\u4ece1\u7d2f\u52a0\u5230\u8be5\u6570\uff0c\u65e0\u9700\u8003\u8651\u5143\u7d20\u53d1\u751f\u4fee\u6539\u95ee\u9898<br \/>\n\u2461 \u8fb9\u8bfb\u5165\u6570\u636e\u8fb9\u7d2f\u52a0\uff0c\u4e00\u6b21\u6027\u8ba1\u7b97\u51fa\u6bcf\u4e2a\u4f4d\u7f6e\u7684\u524d\u7f00\u548c\u5e76\u4fdd\u5b58\u7ed3\u679c\uff0c\u67e5\u8be2\u65f6\u76f4\u63a5\u8bfb\u53d6\uff0c\u4efb\u4e00\u5143\u7d20\u53d1\u751f\u4fee\u6539\u91cd\u65b0\u8ba1\u7b97\u540e\u7eed\u6240\u6709\u524d\u7f00\u548c<br \/>\n\u2462 \u6784\u9020\u6811\u72b6\u6570\u7ec4\uff0c\u8ba1\u7b97\u548c\u65f6\u5206\u89e3\u4e3a\u5c0f\u533a\u95f4\u548c\uff0c\u66f4\u65b0\u5b50\u533a\u95f4\u65f6\u540c\u65f6\u66f4\u65b0\u7236\u533a\u95f4<\/p>\n<table>\n<thead>\n<tr>\n<th style=\"text-align: left;\">\u65b9\u6848<\/th>\n<th style=\"text-align: left;\">\u6784\u9020\u590d\u6742\u5ea6<\/th>\n<th style=\"text-align: left;\">\u4e00\u6b21\u67e5\u8be2<\/th>\n<th style=\"text-align: left;\">M\u6b21\u67e5\u8be2<\/th>\n<th style=\"text-align: left;\">\u4e00\u6b21\u4fee\u6539<\/th>\n<th style=\"text-align: left;\">M\u6b21\u4fee\u6539<\/th>\n<\/tr>\n<\/thead>\n<tbody>\n<tr>\n<td style=\"text-align: left;\">\u2460<\/td>\n<td style=\"text-align: left;\"><code>$$\\scriptsize O(N)$$<\/code><\/td>\n<td style=\"text-align: left;\"><code>$$\\scriptsize O(N)$$<\/code><\/td>\n<td style=\"text-align: left;\"><code>$$\\scriptsize O(MN)$$<\/code><\/td>\n<td style=\"text-align: left;\"><code>$$\\scriptsize O(1)$$<\/code><\/td>\n<td style=\"text-align: left;\"><code>$$\\scriptsize O(M)$$<\/code><\/td>\n<\/tr>\n<tr>\n<td style=\"text-align: left;\">\u2461<\/td>\n<td style=\"text-align: left;\"><code>$$\\scriptsize O(N)$$<\/code><\/td>\n<td style=\"text-align: left;\"><code>$$\\scriptsize O(1)$$<\/code><\/td>\n<td style=\"text-align: left;\"><code>$$\\scriptsize O(M)$$<\/code><\/td>\n<td style=\"text-align: left;\"><code>$$\\scriptsize O(N)$$<\/code><\/td>\n<td style=\"text-align: left;\"><code>$$\\scriptsize O(MN)$$<\/code><\/td>\n<\/tr>\n<tr>\n<td style=\"text-align: left;\">\u2462<\/td>\n<td style=\"text-align: left;\"><code>$$\\scriptsize O(N)$$<\/code>(\u6700\u4f18)<\/td>\n<td style=\"text-align: left;\"><code>$$\\scriptsize O(log_2N)$$<\/code><\/td>\n<td style=\"text-align: left;\"><code>$$\\scriptsize O(Mlog_2N)$$<\/code><\/td>\n<td style=\"text-align: left;\"><code>$$\\scriptsize O(log_2N)$$<\/code><\/td>\n<td style=\"text-align: left;\"><code>$$\\scriptsize O(Mlog_2N)$$<\/code><\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<p>\u65e0\u9700\u4fee\u6539\u65f6\u9996\u9009 \u2461\uff0cN\u8f83\u5927\u6216\u6d89\u53ca\u591a\u6b21\u4fee\u6539\u540e\u518d\u67e5\u8be2\u65f6\uff0c\u91c7\u7528\u6811\u72b6\u6570\u7ec4\u5f00\u9500\u66f4\u5c0f<\/p>\n<pre><code class=\"language-cpp\">const int N = 1000;\nint bit[N + 1];\n\n\/\/ \u533a\u95f4\u67e5\u8be2\uff1a\u5206\u89e3\u8ba1\u7b97\u533a\u95f4\u548c\nint sum(int i) {\n    int s = 0;\n    while (i &gt; 0) {\n        s += bit[i];\n        i -= lowbit(i);\n    }\n    return s;\n}\n\n\/\/ \u5355\u70b9\u4fee\u6539\uff1a\u8fd0\u7b97\u8fc7\u7a0b\u4e2d\u6539\u52a8\u6570\u636e\u65f6\u4fee\u6539\u7236\u5b50\u533a\u95f4\u548c\u6216\u521d\u59cb\u5316bit\nvoid add(int i, int num) {\n    while (i &lt;= N) {\n        bit[i] += num;\n        i += lowbit(i);\n    }\n}\n\nint main() {\n    int a, ask;\n    memset(bit, 0, sizeof(bit));\n    for (int i = 1; i &lt;= N; i++) {\n        scanf(&quot;%d&quot;, &amp;a);\n        add(i, a);\n    }\n    while (~scanf(&quot;%d&quot;, &amp;ask))\n        printf(&quot;%d&quot;, sum(ask));\n    return 0;\n}<\/code><\/pre>\n<h3>\u533a\u95f4\u548c<\/h3>\n<p>\u533a\u95f4 <code>$$\\scriptsize [i,j]$$<\/code> \u7684\u5143\u7d20\u548c <code>$$\\scriptsize sum(a[1\uff0cj]) = suffix(1,j) - suffix(1,i-1)$$<\/code>\uff0c\u5373\u524d\u7f00\u548c\u5dee\u503c<\/p>\n<pre><code class=\"language-cpp\">...\nint main() {\n    ...\n    while (~scanf(&quot;%d&quot;, &amp;i, &amp;j))\n        printf(&quot;%d&quot;, sum(j) - sum(i - 1));\n    return 0;\n}<\/code><\/pre>\n<h3>\u524d\u7f00\u6700\u5927\u503c<\/h3>\n<p>\u6784\u9020\u6811\u72b6\u6570\u7ec4\u65f6\uff0c\u6240\u6709\u533a\u95f4\u90fd\u5b58\u50a8\u533a\u95f4\u957f\u5ea6\u5185\u7684\u6700\u5927\u503c<br \/>\n\u67e5\u8be2\u6700\u5927\u503c\u65f6\uff0c\u4f9d\u6b21\u5411\u524d\u5e8f\u533a\u95f4\u5bf9\u6bd4\u5bfb\u627e\u6700\u5927\u503c<\/p>\n<pre><code class=\"language-cpp\">const int N = 1000;\nint bit[N + 1];\n\nvoid add(int i, int num) {\n    while(i &lt;= N) {\n        if(num &gt; bit[i]) bit[i] = num;\n        i += lowbit(i);\n    }\n}\n\nint sum(int i) {\n    int max = bit[i];\n    while(i &gt; 0) {\n        i -= lowbit(i);\n        if(i &gt; 0 &amp;&amp; max &lt; bit[i])\n            max = bit[i];\n    }\n    return max;\n}\n\nint main() {\n    int a, ask;\n    memset(bit, 0, sizeof(bit));\n    for (int i = 1; i &lt;= N; i++) {\n        scanf(&quot;%d&quot;, &amp;a);\n        add(i, a);\n    }\n    while (~scanf(&quot;%d&quot;, &amp;ask))\n        printf(&quot;%d&quot;, sum(ask));\n    return 0;\n}<\/code><\/pre>\n<h3>\u9006\u5e8f\u6570<\/h3>\n<p>\u8ba1\u7b97\u9006\u5e8f\u6570\u7684\u4e09\u79cd\u65b9\u6848<br \/>\n\u2460 \u6734\u7d20\u65b9\u6cd5\uff0c\u4e24\u5c42\u5faa\u73af\u9010\u4e2a\u5411\u540e\u626b\u63cf\u66f4\u5c0f\u503c\uff0c\u65f6\u95f4\u590d\u6742\u5ea6 <code>$$\\scriptsize O(N^2)$$<\/code>\uff0c\u672a\u5229\u7528\u4efb\u4f55\u5df2\u8ba1\u7b97\u4fe1\u606f<br \/>\n\u2461 \u5f52\u5e76\u6392\u5e8f\uff0c\u53ef\u5229\u7528\u5f52\u5e76\u65f6\u7684\u4e24\u4e2a\u6709\u5e8f\u5b50\u5e8f\u5217\u957f\u5ea6\u8ba1\u7b97\u9006\u5e8f\u6570\u51cf\u5c11\u8ba1\u7b97\u590d\u6742\u5ea6\uff0c\u65f6\u95f4\u590d\u6742\u5ea6 <code>$$\\scriptsize O(Nlog_2N)$$<\/code><br \/>\n\u2462 \u6811\u72b6\u6570\u7ec4\uff0c\u5229\u7528\u524d\u7f00\u548c\u601d\u60f3\uff0c\u57fa\u4e8e\u5df2\u8ba1\u7b97\u533a\u95f4\u7ed3\u679c\u6765\u8ba1\u7b97\u65b0\u7684\u9006\u5e8f\u6570\uff0c\u65f6\u95f4\u590d\u6742\u5ea6 <code>$$\\scriptsize O(Nlog_2N)$$<\/code>\uff0c\u8be6\u6790\u5982\u4e0b<\/p>\n<p>\u6c42\u89e3\u9006\u5e8f\u6570\u7684\u51e0\u4e2a\u5173\u952e<br \/>\na\uff09\u5982\u4f55\u5224\u65ad\u548c\u7edf\u8ba1\u9006\u5e8f\u5bf9\u6570\u91cf\uff1a\u5e8f\u5217\u4e2d\u67d0\u6570\u4e0e\u5e8f\u5217\u7ec4\u6210\u7684\u9006\u5e8f\u5bf9\u6570\u91cf\u7b49\u4e8e <strong>\u4f4d\u4e8e\u5f53\u524d\u6570\u540e\u4fa7<\/strong> \u4e14 <strong>\u5c0f\u4e8e\u5f53\u524d\u6570<\/strong> \u7684\u6570\u5b57\u7684\u6570\u91cf<br \/>\nb\uff09\u5982\u4f55\u89e3\u51b3\u5f53\u524d\u6570\u540e\u4fa7\u95ee\u9898\uff1a\u82e5\u5012\u5e8f\u8bfb\u5165\u5e8f\u5217\uff0c<strong>\u65e9\u5148\u8bfb\u5165\u7684\u6570\u662f\u540e\u4fa7\u6570<\/strong>\uff0c\u8bfb\u5165\u65b0\u6570\u65f6\u540e\u4fa7\u6240\u6709\u6570\u5747\u5df2\u8bfb\u53d6\u5b8c\u6bd5<br \/>\nc\uff09\u5982\u4f55\u7edf\u8ba1\u5c0f\u4e8e\u5f53\u524d\u6570\u6570\u91cf\uff1a\u82e5\u7528\u4e00\u6570\u7ec4\u8bb0\u5f55\u5404\u6570\u51fa\u73b0\u6b21\u6570\uff0c\u5219\u5c0f\u4e8e\u5f53\u524d\u6570 <code>$$\\scriptsize i$$<\/code> \u7684\u6570\u5b57\u603b\u6570\u5c31\u662f\u533a\u95f4 <code>$$\\scriptsize [1,i-1]$$<\/code> \u7684 <strong>\u524d\u7f00\u548c<\/strong>\u3002\u56e0\u6b64\u4ee5\u7d22\u5f15\u4ee3\u8868\u6bcf\u4e2a\u6570\uff0c\u503c\u4ee3\u8868\u8be5\u533a\u95f4\u7684\u5185\u7684\u6570\u5b57\u8ba1\u6570\u6765\u6784\u5efa\u6811\u72b6\u6570\u7ec4<br \/>\n*\uff09 \u56e0\u6b64\u6bcf\u8bfb\u5165\u4e00\u4e2a\u6570\u5c31\u5411\u524d\u6c42\u524d\u7f00\u548c\uff0c\u5b9e\u5219\u68c0\u7d22\u8be5\u6570\u540e\u4fa7\u5c0f\u4e8e\u8be5\u6570\u7684\u4e2a\u6570\u3002\u524d\u7f00\u548c\u5229\u7528\u5df2\u8ba1\u7b97\u7ed3\u679c\u56e0\u800c\u964d\u4f4e\u4e86\u590d\u6742\u5ea6\u3002\u6bcf\u6b21\u6c42\u53d6\u5b8c\u6bd5\u90fd\u66f4\u65b0\u8bfb\u5165\u6570\u6240\u5728\u7684\u6811\u72b6\u6570\u7ec4\u533a\u95f4\u8ba1\u6570\u3002<\/p>\n<p>\u4f8b\u5012\u5e8f\u8bfb\u5165\u5e8f\u5217 <code>$$\\scriptsize arr: 3,2,5,1,4$$\uff0c\u521d\u59cb <\/code>$$\\scriptsize bit: 0,0,0,0,0$$`<br \/>\n1\uff09\u8bfb\u5165 <code>$$\\scriptsize 4$$<\/code>\uff0c\u67e5\u8be2\u5e8f\u5217\u4e2d <code>$$\\scriptsize 4$$<\/code> \u540e\u4fa7 <code>$$\\scriptsize \\lt4$$<\/code> \u7684\u6570\u5b57\u6570\u91cf\uff0c<br \/>\n\u5373\u67e5\u8be2\u4e4b\u524d\u8bfb\u5165\u7684\u5176\u4ed6 <code>$$\\scriptsize \\lt4$$<\/code> \u7684\u6570\u5b57\u6570\u91cf\uff0c<br \/>\n\u5373\u5411\u524d\u5e8f <code>$$\\scriptsize bit$$<\/code> \u533a\u95f4\u67e5\u8be2 <code>$$\\scriptsize sum(4-1)=bit(3)+bit(2)=0$$<\/code>,<br \/>\n\u5c06\u8ba1\u6570\u66f4\u65b0\u5230\u533a\u95f4 <code>$$\\scriptsize bit(4) = 0 +1 = 1$$<\/code><br \/>\n<code>$$\\scriptsize bit: 0,0,0,0,0 \\Rightarrow bit: 0,0,0,1,0$$<\/code><br \/>\n2\uff09\u8bfb\u5165 <code>$$\\scriptsize 1$$<\/code>\uff0c\u67e5\u8be2 <code>$$\\scriptsize sum(1-1)=bit(0)=0$$<\/code>\uff0c\u6ca1\u6709 <code>$$\\scriptsize \\lt1$$<\/code> \u7684\u6570\uff0c<br \/>\n\u66f4\u65b0  <code>$$\\scriptsize 1$$<\/code> \u6240\u5728\u7684\u7236\u5b50\u533a\u95f4 <code>$$\\scriptsize bit(1)$$<\/code>\u3001<code>$$\\scriptsize bit(2)$$<\/code>\u3001<code>$$\\scriptsize bit(4)$$<\/code> \u8ba1\u6570\u52a0\u4e00<br \/>\n<code>$$\\scriptsize bit: 0,0,0,1,0 \\Rightarrow bit: 1,1,0,2,0$$<\/code><br \/>\n3\uff09\u8bfb\u5165 <code>$$\\scriptsize 5$$<\/code>\uff0c<code>$$\\scriptsize sum(5-1)=bit(4)=2$$<\/code>,<br \/>\n<code>$$\\scriptsize bit: 1,1,0,2,0 \\Rightarrow bit: 1,1,0,2,1$$<\/code><br \/>\n4\uff09\u8bfb\u5165 <code>$$\\scriptsize 2$$<\/code>\uff0c<code>$$\\scriptsize sum(2-1)=bit(1)=1$$<\/code>,<br \/>\n<code>$$\\scriptsize bit: 1,1,0,2,1 \\Rightarrow bit: 1,2,0,3,1$$<\/code><br \/>\n5\uff09\u8bfb\u5165 <code>$$\\scriptsize 3$$<\/code>\uff0c<code>$$\\scriptsize sum(3-1)=bit(2)=2$$<\/code>,<br \/>\n<code>$$\\scriptsize bit: 1,2,0,3,1 \\Rightarrow bit: 1,2,1,4,1$$<\/code><br \/>\n\u6b64\u65f6\u67e5\u8be2 <code>$$\\scriptsize sum(5)=bit(5)+bit(4)=1+4=5$$<\/code> \u5373\u4e3a\u7b54\u6848<br \/>\n\u7531\u4e8e\u5176\u5012\u5e8f\u8bfb\u53d6\u7684\u7279\u6b8a\u6027\uff0c\u5904\u7406\u5b8c\u6bd5\u6570\u7684\u9006\u5e8f\u6570\u4e00\u5b9a\u4e0d\u4f1a\u518d\u53d1\u751f\u53d8\u5316\uff0c\u53ef\u5728\u6bcf\u6b21\u8ba1\u7b97\u524d\u7f00\u548c\u65f6\u5373\u7d2f\u52a0\u5165\u7ed3\u679c<\/p>\n<pre><code class=\"language-cpp\">const int N = 100;\nint bit[N], a[N];\n\nvoid add(int i) {\n    while(i &lt;= N) {\n        bit[i]++;\n        i += lowbit(i);\n    }\n}\n\nint sum(int i) {\n    int s = 0;\n    while(i &gt; 0) {\n        s += bit[i];\n        i -= lowbit(i);\n    }\n    return s;\n}\n\nint main() {\n    int ans = 0;\n    memset(bit, 0, sizeof(bit));\n    for(int i = 1; i &lt;= N; i++)\n        scanf(&quot;%d&quot;, &amp;a[i]);\n\n    for(int i = N; i &gt; 0; i--) {\n        ans += sum(a[i] - 1);\n        add(a[i]);\n    }\n\n    printf(&quot;%d&quot;, ans);\n    return 0;\n}<\/code><\/pre>\n<h3>\u4e8c\u7ef4\u524d\u7f00\u548c<\/h3>\n<h3>\u533a\u95f4\u7b2ck\u5927\u503c<\/h3>\n<h2>lowbit\u4e3a\u4ec0\u4e48\u6709\u6548<\/h2>\n","protected":false},"excerpt":{"rendered":"<p>\u7efc\u8ff0 \u6811\u72b6\u6570\u7ec4\u662f\u89e3\u51b3 \u524d\u7f00 \u76f8\u5173\u95ee\u9898\u7684\u4e00\u79cd\u6570\u636e\u7ed3\u6784 \u5728\u524d\u7f00\u76f8\u5173\u95ee\u9898\u4e2d\u53ef\u5229\u7528\u524d\u5e8f\u5df2\u8ba1\u7b97\u7ed3\u679c\u907f\u514d\u91cd\u590d\u8ba1\u7b97\u964d\u4f4e\u590d\u6742\u5ea6 &hellip; <\/p>\n<p class=\"link-more\"><a href=\"http:\/\/139.196.114.170\/?p=1820\" class=\"more-link\">\u7ee7\u7eed\u9605\u8bfb<span class=\"screen-reader-text\">\u201c\u524d\u7f00\u95ee\u9898\u9ad8\u6548\u89e3\u6cd5 &#8211; \u6811\u72b6\u6570\u7ec4\u8be6\u6089\u201d<\/span><\/a><\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":[],"categories":[12],"tags":[],"jetpack_featured_media_url":"","_links":{"self":[{"href":"http:\/\/139.196.114.170\/index.php?rest_route=\/wp\/v2\/posts\/1820"}],"collection":[{"href":"http:\/\/139.196.114.170\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"http:\/\/139.196.114.170\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"http:\/\/139.196.114.170\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"http:\/\/139.196.114.170\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=1820"}],"version-history":[{"count":36,"href":"http:\/\/139.196.114.170\/index.php?rest_route=\/wp\/v2\/posts\/1820\/revisions"}],"predecessor-version":[{"id":2744,"href":"http:\/\/139.196.114.170\/index.php?rest_route=\/wp\/v2\/posts\/1820\/revisions\/2744"}],"wp:attachment":[{"href":"http:\/\/139.196.114.170\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=1820"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"http:\/\/139.196.114.170\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=1820"},{"taxonomy":"post_tag","embeddable":true,"href":"http:\/\/139.196.114.170\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=1820"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}