二分區間

#include <iostream> using namespace std; int lower_bound(int* a, int n, int x) { int l = 0, r = n - 1; while(l < r) { int mid = l + r >> 1; if(a[mid] >= x) r = mid; else l = mid + 1; } return l; } int upper_bound(int* a, int n, int x) { int l = 0, r = n - 1; while(l < r) { int mid = l + r + 1 >> 1; if(a[mid] <= x) l = mid; else r = mid - 1; } return l; } int main() { int a[] = { 1, 2, 4, 4, 5}; int n = sizeof(a) / sizeof(a[0]), x = 4; cout << lower_bound(a, n, x) << " " << upper_bound(a, n, x) << endl; return 0; }