LeetCode Search for Range


class Solution {

private:

    int getDirection(int A[], int idx, int target, bool isDefaultBack) {

        int r = A[idx] - target;

        if (r == 0) {

            r = isDefaultBack ? -1 : 1;

        }

        return r;

    }

    int getFirstValueIndex(int A[], int n, int target, bool isFromBack) {

        int p = -1;

        int q = n;

        while (p + 1 < q) {

            int mid_idx = (p + q) / 2;

            int where = getDirection(A, mid_idx, target, isFromBack);

            if (where < 0) {

                p = mid_idx;

            } else {

                q = mid_idx;

            }

        }

        if (p != -1 && A[p] != target) {

            p = -1;

        }

        if (q == n || A[q] != target) {

            q = -1;

        }

        return isFromBack ? p : q;

    }

public:

    vector<int> searchRange(int A[], int n, int target) {

        vector<int> res;

        res.push_back(getFirstValueIndex(A, n, target, false));

        res.push_back(getFirstValueIndex(A, n, target, true));

        return res;

    }

};

进行两次二分查找，一次找upper bound一次找lower bound，如果线性查找的化就不符合要求了。

LeetCode Search for Range,布布扣,bubuko.com

时间： 2024-10-07 15:21:17

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