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Program to get next integer permutation of a number in C++
Suppose we have a number n, we have to find the next bigger permutation of its digits. When n is already in its largest permutation, then rotate it down to the smallest permutation.
So, if the input is like n = 319, then the output will be 391.
To solve this, we will follow these steps −
Define a function makeArray(), this will take x,
Define an array ret
while x is non-zero, do −
insert x mod 10 at the end of ret
x := x / 10
reverse the array ret
return ret
Define a function combine(), this will take an array v,
ret := 0
for each element i in v
ret := ret * 10
ret := ret + i
return ret
Define a function getIndex(), this will take an array v,
ret := -1
for initialize i := size of v, when i >= 1, update (decrease i by 1), do −
if v[i] > v[i - 1], then −
ret := i
Come out from the loop
if ret is not equal to -1, then −
x := v[ret - 1]
idx := ret
for initialize j := ret + 1, when j < size of v, update (increase j by 1), do −
if v[j] < v[idx] and v[j] > x, then −
idx := j
exchange v[ret - 1] and v[idx]
return ret
From the main method do the following −
Define an array v := makeArray(num)
idx := getIndex(v)
if idx is same as -1, then −
sort the array v
Otherwise
sort the array v
return combine(v)
Example
Let us see the following implementation to get better understanding −
#include <bits/stdc++.h>
using namespace std;
class Solution {
public:
vector<int> makeArray(int x) {
vector<int> ret;
while (x) {
ret.push_back(x % 10);
x /= 10;
}
reverse(ret.begin(), ret.end());
return ret;
}
int combine(vector<int>& v) {
int ret = 0;
for (int i : v) {
ret *= 10;
ret += i;
}
return ret;
}
int getIndex(vector& v) {
int ret = -1;
for (int i = v.size() - 1; i >= 1; i--) {
if (v[i] > v[i - 1]) {
ret = i;
break;
}
}
if (ret != -1) {
int x = v[ret - 1];
int idx = ret;
for (int j = ret + 1; j < v.size(); j++) {
if (v[j] < v[idx] && v[j] > x) {
idx = j;
}
}
swap(v[ret - 1], v[idx]);
}
return ret;
}
int solve(int num) {
vector<int> v = makeArray(num);
int idx = getIndex(v);
if(idx == -1) {
sort(v.begin(), v.end());
}
else {
sort(v.begin() + idx, v.end());
}
return combine(v);
}
};
int solve(int n) {
return (new Solution())->solve(n);
}
int main(){
int n = 319;
cout << solve(n);
}Input
319
Output
391
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