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31-next-permutation/31-next-permutation.c

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+int cmpInt(const void *a, const void *b) {
+    const int *ia = a;
+    const int *ib = b;
+    return *ia - *ib;
+}
+
+void nextPermutation(int* nums, int numsSize){
+    int firstDecrI = -1; 
+    for (int i = numsSize - 2; i >= 0; --i) {
+        if (nums[i] < nums[i + 1]) {
+            firstDecrI = i;
+            break;
+        }
+    }
+    
+    // Last permutation edge case
+    if (firstDecrI == - 1) {
+        qsort(nums, numsSize, sizeof(int), cmpInt);
+        return;
+    }
+    
+    // place next largest num into nums[firstDecrI]
+    int nextHighest = INT_MAX;
+    int nextHighestI = -1;
+    for (int i = firstDecrI + 1; i < numsSize; ++i) {
+        if (nums[firstDecrI] < nums[i] && nums[i] < nextHighest) {
+            nextHighest = nums[i];
+            nextHighestI = i;
+        }
+    }
+    int tmp = nums[firstDecrI];
+    nums[firstDecrI] = nums[nextHighestI];
+    nums[nextHighestI] = tmp;
+    
+    // sort nums[firstDecrI + 1...numsSize - 1]
+    qsort(nums + firstDecrI + 1, numsSize - firstDecrI - 1, sizeof(int), cmpInt);
+    
+}