二分查找

class Solution {
    public static void main(String[] args) {
//        System.out.println(new Solution().find132pattern(new int[]{7, 6, 5, 1, 2, 4, 3}));
        int[] arr = {1, 2, 2, 2, 2, 3, 3, 4,5,5,5};
        System.out.println(new Solution().left_bound(arr, 1));
        System.out.println(new Solution().left_bound2(arr, 1));
        System.out.println(new Solution().right_bound(arr, 1));
        System.out.println(new Solution().right_bound2(arr, 1));
        System.out.println(new Solution().binarySearch(arr, 1));
    }

int left_bound(int[] nums, int target) {
    if (nums.length == 0) {
        return -1;
    }
    int left = 0;
    int right = nums.length; // 注意

    while (left < right) { // 注意
        int mid = (left + right) / 2;
        if (nums[mid] == target) {
            right = mid;
        } else if (nums[mid] < target) {
            left = mid + 1;
        } else if (nums[mid] > target) {
            right = mid; // 注意
        }
    }
    return left;
}
int left_bound2(int[] nums, int target) {
    if (nums.length == 0) {
        return -1;
    }
    int left = 0;
    int right = nums.length-1; // 注意

    while (left <= right) { // 注意
        int mid = (left + right) / 2;
        if (nums[mid] == target) {
            right = mid-1;
        } else if (nums[mid] < target) {
            left = mid + 1;
        } else if (nums[mid] > target) {
            right = mid-1; // 注意
        }
    }
    return left;
}

int right_bound(int[] nums, int target) {
    if (nums.length == 0) {
        return -1;
    }
    int left = 0, right = nums.length;

    while (left < right) {
        int mid = (left + right) / 2;
        if (nums[mid] == target) {
            left = mid + 1; // 注意
        } else if (nums[mid] < target) {
            left = mid + 1;
        } else if (nums[mid] > target) {
            right = mid;
        }
    }
    return left - 1; // 注意
}
int right_bound2(int[] nums, int target) {
    if (nums.length == 0) {
        return -1;
    }
    int left = 0, right = nums.length-1;

    while (left <= right) {
        int mid = (left + right) / 2;
        if (nums[mid] == target) {
            left = mid+1; // 注意
        } else if (nums[mid] < target) {
            left = mid+1;
        } else if (nums[mid] > target) {
            right = mid-1;
        }
    }
    return left-1; // 注意
}

int binarySearch(int[] nums, int target) {
    int left = 0;
    int right = nums.length - 1; // 注意

    while (left <= right) { // 注意
        int mid = (right + left) / 2;
        if (nums[mid] == target) {
            return mid;
        } else if (nums[mid] < target) {
            left = mid + 1; // 注意
        } else if (nums[mid] > target) {
            right = mid - 1; // 注意
        }
    }
    return -1;
}
}
参考：https://www.zhihu.com/question/36132386/answer/712269942