Binary search is a famous question in algorithm. For a given sorted array (ascending order) and a target number, find the first index of this number in O(log n) time complexity. 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.
public class BinarySearch { public int binarySearch(int[] A, int target) { if (A.length == 0) return -1; int start = 0; int end = A.length - 1; int mid; while (start + 1 < end) { mid = start + (end - start) / 2; if (A[mid] == target) end = mid; else if (A[mid] < target) start = mid; else if (A[mid] > target) end = mid; } if (A[start] == target) return start; if (A[end] == target) return end; return -1; } }
原文：http://www.cnblogs.com/luochuanghero/p/4279057.html