也叫折半查找

NC160

无重复数字的升序数组的二分查找

public int search (int[] nums, int target) {// write code hereint left = 0, right = nums.length - 1;int temp;while (left <= right){temp = (left + right)/2;if (nums[temp] == target){return temp;}else if (nums[temp] < target){left = temp + 1;}else {right = temp - 1;}}return -1;}//也可以用递归的方法，不过方法参数要增加两项，即分出来的左右边界left,right//折半查找-有序数组public int find(int[] nums, int left, int right, int target){int temp = (left + right)/2;if (left > right){return -1;return;}if (nums[temp] == target){return temp;}else if(nums[temp] > target){find(nums, left, temp - 1, target);}else{find(nums, temp + 1, right, target);}}

NC105

有重复数字的升序数组的二分查找

int right = nums.length - 1, left = 0, temp;while (left <= right){temp = (left + right)/2;if (nums[temp] == target){//添加这一句while即可，找到target之后往前找到相等的第一个出现的位置，注意判断越界问题while((temp - 1 >= 0) && (nums[temp-1] == nums[temp]))temp = temp - 1;return temp;}else if (nums[temp] < target){left = temp + 1;}else {right = temp - 1;}}return -1;