"Min Stack"

Author: lennylxx

README.md

@@ -39,7 +39,7 @@ them with C++ Language.
 | 158 | [Read N Characters Given Read4 II - Call multiple times]     |                    |
 | 157 | [Read N Characters Given Read4]                              |                    |
 | 156 | [Binary Tree Upside Down]                                    |                    |
-| 155 | [Min Stack]                                                  |                    |
+| 155 | [Min Stack]                                                  | [C](src/155.c)     |
 | 154 | [Find Minimum in Rotated Sorted Array II]                    |                    |
 | 153 | [Find Minimum in Rotated Sorted Array]                       |                    |
 | 152 | [Maximum Product Subarray]                                   | [C](src/152.c)     |

src/155.c

@@ -0,0 +1,113 @@
+#include <stdio.h>
+#include <stdlib.h>
+
+typedef struct StackNode {
+    int val;
+    struct StackNode *next;
+} StackNode;
+
+typedef struct MinStack {
+    int size;
+    StackNode *top;
+    StackNode *min;
+} MinStack;
+
+void minStackCreate(MinStack *stack, int maxSize) {
+    /* I implement a linked stack, so I don't need maxSize */
+    if (stack) {
+        stack->min = NULL;
+        stack->top = NULL;
+        stack->size = 0;
+    }
+}
+
+void minStackPush(MinStack *stack, int element) {
+    if (stack) {
+        StackNode *new_node = (StackNode *)calloc(1, sizeof(StackNode));
+        new_node->val = element;
+        new_node->next = stack->top;
+        stack->top = new_node;
+        stack->size++;
+        /* update min pointer */
+        StackNode *new_min = (StackNode *)calloc(1, sizeof(StackNode));
+        new_min->val = element;
+        new_min->next = stack->min;
+
+        if (stack->min) {
+            if (stack->min->val >= element){
+                stack->min = new_min;
+            }
+        }
+        else {
+            stack->min = new_min;
+        }
+    }
+}
+
+void minStackPop(MinStack *stack) {
+    if (stack && stack->top) {
+        StackNode *t = stack->top;
+        stack->top = stack->top->next;
+        if (stack->min && t <= stack->min) {
+            StackNode *m = stack->min;
+            stack->min = stack->min->next;
+            free(m);
+        }
+        stack->size--;
+        free(t);
+    }
+}
+
+int minStackTop(MinStack *stack) {
+    if (stack && stack->top) {
+        return stack->top->val;
+    }
+    return 0;
+}
+
+int minStackGetMin(MinStack *stack) {
+    if (stack && stack->min) {
+        return stack->min->val;
+    }
+    return 0;
+}
+
+void minStackDestroy(MinStack *stack) {
+    if (stack) {
+        while (stack->size != 0) {
+            minStackPop(stack);
+        }
+        while (stack->min != NULL) {
+            StackNode *m = stack->min;
+            stack->min = stack->min->next;
+            free(m);
+        }
+        /**
+         *free(stack);
+         *stack = NULL;
+         */
+    }
+}
+
+int main() {
+    MinStack stack;
+    minStackCreate(&stack, 10);
+    int i;
+    for (i = 0; i < 5; i++) {
+        minStackPush(&stack, i);
+    }
+
+    printf("top: %d\n", minStackTop(&stack));
+    printf("min: %d\n", minStackGetMin(&stack));
+
+    for (i = 1; i < 5; i++) {
+        minStackPush(&stack, -i);
+    }
+
+    printf("top: %d\n", minStackTop(&stack));
+    printf("min: %d\n", minStackGetMin(&stack));
+
+    minStackDestroy(&stack);
+
+    return 0;
+}