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#include <bits/stdc++.h>
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// 需要仔细研究一下lower_bound,upper_bound,还有手动二分的差别，这个细节很重要
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// https://www.cnblogs.com/linsinan1995/p/13620590.html
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using namespace std;
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const int N = 110;
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int a[9] = {1, 2, 2, 3, 3, 3, 4, 6, 7};
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// 区间[l, r]被划分成[l, mid]和[mid + 1, r]时使用：
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int bsearch_1(int l, int r, int x) {
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while (l < r) {
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int mid = (l + r) >> 1;
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if (a[mid] >= x)
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r = mid; // check()判断mid是否满足性质
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else
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l = mid + 1;
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}
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return l;
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}
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// 区间[l, r]被划分成[l, mid - 1]和[mid, r]时使用：
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int bsearch_2(int l, int r, int x) {
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while (l < r) {
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int mid = (l + r + 1) >> 1;
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if (a[mid] <= x)
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l = mid;
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else
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r = mid - 1;
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}
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return l;
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}
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int main() {
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printf("%d\n", lower_bound(a, a + 9, 3) - a); // 3
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printf("%d\n", upper_bound(a, a + 9, 3) - a); // 5
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printf("%d\n", bsearch_1(0, 8, 3));
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printf("%d\n", bsearch_2(0, 8, 3));
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return 0;
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} |
