【数据结构和算法】三种解决方式

往左边逼近

    public int search(int[] nums, int target) {
        //边界条件判断
        if (nums == null || nums.length == 0)
            return -1;
        int left = 0;
        int right = nums.length - 1;
        while (left < right) {
            int mid = left + (right - left) / 2;
            if (nums[mid] < target) {
                left = mid + 1;
            } else {
                right = mid;
            }
        }
        return nums[left] == target ? left : -1;
    }

查找之后往左边继续查找

    public int search(int[] nums, int target) {
        if (nums == null || nums.length == 0)
            return -1;
        int left = 0;
        int right = nums.length - 1;
        while (left <= right) {
            int mid = left + (right - left) / 2;
            if (nums[mid] < target) {
                left = mid + 1;
            } else if (nums[mid] > target) {
                right = mid - 1;
            } else {
                //找到之后，往左边找
                while (mid != 0 && nums[mid] == nums[mid - 1])
                    mid--;
                return mid;
            }
        }
        return -1;
    }

递归解决

    public int search(int[] nums, int target) {
        if (nums == null || nums.length == 0)
            return -1;
        return helper(nums, target, 0, nums.length - 1);
    }

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

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