LintCode First Position of Target

找指定target的最左位置。

 

class Solution {
    /**
     * @param nums: The integer array.
     * @param target: Target to find.
     * @return: The first position of target. Position starts from 0.
     */
    public int binarySearch(int[] nums, int target) {
        if(nums == null) return -1;
        if(nums.length == 0) return -1;
        int left = 0; int right = nums.length -1; 
        
        while(left + 1 < right){
            int mid = (left + right) / 2;
            if(nums[mid] < target){
                left = mid;
            }
            else if(nums[mid] > target){
                right = mid;
            }
            else if(nums[mid] == target){
                right = mid;
            }
        }
        if(nums[left] == target){
            return left;
        }
        else if(nums[right] == target){
            return right;
        }
        else return -1;
    }
}