Merge pull request #544 from swainsubrat/master

Lexicographic rank of a string

Author: probot-auto-merge[bot]

Strings/lexicographicRank.cpp

@@ -0,0 +1,68 @@
+/*
+Input : str[] = "acb"
+Output : Rank = 2
+
+Input : str[] = "string"
+Output : Rank = 598
+
+Input : str[] = "cba"
+Output : Rank = 6
+*/
+
+// C++ program to find lexicographic rank 
+// of a string 
+#include <bits/stdc++.h> 
+#include <string.h> 
+  
+using namespace std; 
+// A utility function to find factorial of n 
+int fact(int n) 
+{ 
+    return (n <= 1) ? 1 : n * fact(n - 1); 
+} 
+  
+// A utility function to count smaller characters on right 
+// of arr[low] 
+int findSmallerInRight(char* str, int low, int high) 
+{ 
+    int countRight = 0, i; 
+  
+    for (i = low + 1; i <= high; ++i) 
+        if (str[i] < str[low]) 
+            ++countRight; 
+  
+    return countRight; 
+} 
+  
+// A function to find rank of a string in all permutations 
+// of characters 
+int findRank(char* str) 
+{ 
+    int len = strlen(str); 
+    int mul = fact(len); 
+    int rank = 1; 
+    int countRight; 
+  
+    int i; 
+    for (i = 0; i < len; ++i) { 
+        mul /= len - i; 
+  
+        // count number of chars smaller than str[i] 
+        // fron str[i+1] to str[len-1] 
+        countRight = findSmallerInRight(str, i, len - 1); 
+  
+        rank += countRight * mul; 
+    } 
+  
+    return rank; 
+} 
+  
+// Driver program to test above function 
+int main() 
+{ 
+    char str[] = "string"; 
+    cout << findRank(str); 
+    return 0; 
+} 
+  
+// This code is contributed by Subrat Kumar Swain