First Position of Target

For a given sorted array (ascending order) and a number target , find the first index of this number in time O(log n) complexit Y.

If the target number does not exist in the array, return -1 .

Example

If the array is [1, 2, 3, 3, 4, 5, 10] , for given target 3 , return 2 .

Analysis:
Obviously with binary search, but because we need to find the first one, we have to judge.

1 classSolution {2     /**3 * @param nums:the integer array.4 * @param target:target to find.5 * @return: The first position of target. Position starts from 0.6      */7      Public intBinarySearch (int[] Nums,inttarget) {8         if(Nums = =NULL|| Nums.length = =0)return-1;9         Ten         intStart =0; One         intEnd = Nums.length-1; A          -          while(Start <=end) { -             intMID = start + (End-start)/2; the             if(Nums[mid] = =target) { -                 if(Mid! =0&& Nums[mid-1] ==target) { -End = Mid-1; -}Else { +                     returnmid; -                 } +}Else if(Nums[mid] <target) { AStart = mid +1; at}Else { -End = Mid-1; -             } -         } -         return-1; -     } in}

Reference Please specify Source: cnblogs.com/beiyeqingteng/

First Position of Target