二分查找★★★

解决哪类问题

:::success 线性数组查找指定元素/元素坐标 :::

代码模板

简单版

int bs(int[] arr, int l, int r, int target) { // 找到最靠近target且>=target的index
    while (l < r) {
        int mid = (r - l) / 2 + l;
        if (arr[mid] < target) {
            l = mid + 1;
        } else  {
            r = mid;
        }
    }
    return l;
}

完整版

int findBoundary(int[] nums, int target, int direction) {
        int left = 0, right = nums.length - 1;
        while (left <= right) {
            int mid = left + (right - left) / 2;
            if (nums[mid] < target) {
                // 更新left
                left = mid + 1;
            } else if (nums[mid] > target) {
                // 更新right
                right = mid - 1;
            } else if (nums[mid] == target) {
                if (direction == 0) {
                    // 找左边界，收缩右边界
                    right = mid - 1;
                } else {
                    // 找右边界，收缩左边界
                    left = mid + 1;
                }
            }
        }
        if (direction == 0) {
            if (left >= nums.length || nums[left] != target)
                return -1;
            return left;
        } else {
            if (right < 0 || nums[right] != target)
                return -1;
            return right;
        }
}

复杂度

O(logn)

运用思想

分治

例题