leetcode(31)下一个排列

下一个排列

解题思路：二分查找+数组反转

class Solution {
    public void nextPermutation(int[] nums) {
        int len = nums.length;
        if(len<=1){
            return;
        }
        int i = 0;
        for(i=len-1;i>0;--i){
            if(nums[i]>nums[i-1]){
                int end = erfen(nums,i,len-1,nums[i-1]);
                nums[i-1]=nums[i-1]^nums[end];
                nums[end]=nums[i-1]^nums[end];
                nums[i-1]=nums[i-1]^nums[end];
                reverse(nums, i, len);
                break;
            }
        }
        if(i==0){
            reverse(nums, 0, len);
        }
    }
    public void reverse(int[] nums, int i, int len){
        int leng = i+(len-i)/2;
        for(int k=i;k<leng;++k){
            nums[k] = nums[k]^nums[len-1];
            nums[len-1] = nums[k]^nums[len-1];
            nums[k] = nums[k]^nums[len-1];
            --len;
        }
    }
    public int erfen(int[] nums, int start, int end,int target){
        int mid = 0;
        while(start<=end){
            mid = (start+end)/2;
            if(target>=nums[mid]){
                end = mid -1;
            }else{
                start = mid+1;
            }
        }
        return end;
    }
}