47 lines
1.7 KiB
C++
47 lines
1.7 KiB
C++
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#include <bits/stdc++.h>
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using namespace std;
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int n, m, a[10000] = {-1};
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int main() {
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//输入+输出重定向
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freopen("../1305.txt", "r", stdin);
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//录入数据
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cin >> n >> m;
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for (int i = 1; i <= n; i++) {
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cin >> a[i];
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}
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//m个询问
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for (int i = 1; i <= m; i++) {
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int x;
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cin >> x;
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int left = 1, right = n, mid;
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/*
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用left表示序列的左边界，用right表示序列的右边界，[left，right]组成序列。
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一开始left=1，right=n。序列已经按照升序排好，保证了二分的有序性。
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二分法
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二分的步骤：
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1.去序列区间的中间值mid=(left+right)/2；
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2.判断mid与x的关系，如果a[mid]>x，所以区间[mid,right]直接排除，修改right=mid-1；如果a[mid]<=x，所以区间[left，mid]直接排除，修改right=mid+1；
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3.重复执行二分操作直到left>right。最终循环结束时一定是left=right+1，所以最后的结果为right指向的值。
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4.如果在序列中找不到合适的位置，或者说是在最前面添加上的话，那么right=0,需要将a[0]设置为-1.
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*/
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while (left <= right) { //注意是小于等于
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mid = (left + right) / 2; //取中间值
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if (a[mid] <= x) {
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left = mid + 1; //在右边，则left修改为mid+1
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} else { //在左边，则right修改为mid-1
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right = mid - 1;
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}
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}
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//cout << "left=" << left << ",right=" << right << endl;
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cout << a[right] << endl;
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}
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//关闭文件
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fclose(stdin);
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return 0;
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}
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