Next Permutation

 https://leetcode.com/problems/next-permutation/

 https://www.interviewbit.com/old/problems/next-permutation/

step1> traverse from right to left ,  a[i] < a[i+1]      -->indx1

step2 > traverse from right to left , a[idx2] > a[idx1]

step3 > swap value at idx1 and idx 2

step 4> reverse from idx1+1 to last

class Solution {
public:
    void nextPermutation(vector<int>& num) {
        int n=num.size(),k,l;
        for(k=n-2;k>=0;k--){
            if(num[k]<num[k+1]){
                break;
            }
        }
        if(k<0){
            reverse(num.begin(),num.end());
        }
        else{
            for(l=n-1;l>=k;l--){
                if(num[l]>num[k]){
                    break;
                }
            }
            swap(num[k],num[l]);
            reverse(num.begin()+k+1,num.end());
        }
    }
};