LeetCode34. Find First and Last Position of Element in Sorted Array

题意

• 一个非降序序列, 一个target, 求target在序列中出现的首次和某次位置

解法

• 二分

代码

vector<int> searchRange(vector<int>& nums, int target) {
    int N = nums.size();
    int lo = 0, hi = N;
    int fir = -1, lst = -1;
    while (lo < hi) {
        int mid = lo + (hi - lo) / 2;
        if (nums[mid] == target) {
            fir = mid; hi = mid;
        }
        else if (nums[mid] < target) lo = mid+1;
        else hi = mid;
    }

    lo = 0; hi = N;
    while (lo < hi) {
        int mid = lo + (hi - lo) / 2;
        if (nums[mid] == target) {
            lst = mid; lo = mid+1;
        }
        else if (nums[mid] < target) lo = mid+1;
        else hi = mid;
    }

    return {fir, lst};
}