java permutation code example

Example 1: java permutation

public static boolean next_permutation(int[] arr) {
	int len = arr.length;
	int i = len - 1;

    // 1. find largest i where arr[i - 1] < arr[i]
	while (i > 0) {
		if (arr[i - 1] < arr[i]) break;
    	i--;
  	}

  	if (i <= 0) return false;

  	// 2. find largest j where arr[i - 1] < arr[j] and j >= i
  	int j = len - 1;
  	while (j >= i) {
    	if (arr[i - 1] < arr[j]) break;
    	j--;
  	}

	// 3. swap elements between arr[i-1] and arr[j]
  	swap(i - 1, j, arr);

  	// 4. reverse elements from i to end of array
  	len--;
  	while (i < len) {
    	swap(i, len, arr);
    	len--;
    	i++;
  	}
  	return true;
}

public static void swap(int x, int y, int[] arr) {
  	int temp = arr[x];
  	arr[x] = arr[y];
  	arr[y] = temp;
}

Example 2: find all permutations of a string

void permute(string a, int l, int r)  
{  
    // Base case  
    if (l == r)  
        cout<<a<<endl;  
    else
    {  
        // Permutations made  
        for (int i = l; i <= r; i++)  
        {  
  
            // Swapping done  
            swap(a[l], a[i]);  
  
            // Recursion called  
            permute(a, l+1, r);  
  
            //backtrack  
            swap(a[l], a[i]);  
        }  
    }  
}