思路是用dp动态规划,一开始想只在最小栈结构体里面存一个min变量,不断Push不断更新,然而在最小站pop时,无法确定是否pop的值是不是最小的。思考,只用一个变量肯定无法记录所有最小值状态,至少要搞一个数组。
所以在最小栈结构体里面又存了一个最小值栈来存取最小值,当push的值比当前最小值(存到这个数组栈里)还小时,我们将最小值栈push进这个值,当push的值比当前最小值大时,我们将之前的最小值复制一份push到栈里。
老实说,用C写leetcode对于我这种代码量少的真是一种锻炼,同时练习了链栈和数组栈的实现。同时对于动态规划也加深了理解。
上代码:
#define MAX_VALUES 20001
typedef struct StackNode{
int data;
struct StackNode* next;
}StackNode,*MinStackPtr;
typedef struct {
int min_stack[MAX_VALUES];
int min_stack_top;
int count;
MinStackPtr top;
} MinStack;
/** initialize your data structure here. */
MinStack* minStackCreate() {
MinStack* p=malloc(sizeof(MinStack));
for(int i=0;i<MAX_VALUES;i++){
p->min_stack[i]=INT_MAX;
}
p->min_stack_top=0;
p->count=0;
p->top=NULL;
return p;
}
void minStackPush(MinStack* obj, int x) {
MinStackPtr s=malloc(sizeof(StackNode));
s->data=x;
s->next=obj->top;
obj->top=s;
obj->count++;
if(x <= obj->min_stack[obj->min_stack_top]){
obj->min_stack[++obj->min_stack_top]=x;
}
else{
obj->min_stack[obj->min_stack_top+1]=obj->min_stack[obj->min_stack_top];
obj->min_stack_top++;
}
}
void minStackPop(MinStack* obj) {
obj->min_stack_top--;
if(obj->count==0)
return;
MinStackPtr s=obj->top;
obj->top=obj->top->next;
free(s);
obj->count--;
}
int minStackTop(MinStack* obj) {
return obj->top->data;
}
int minStackMin(MinStack* obj) {
return obj->min_stack[obj->min_stack_top];
}
void minStackFree(MinStack* obj) {
MinStackPtr s=obj->top;
MinStackPtr temp;
while(s){
temp=s;
s=s->next;
free(temp);
}
obj->top=NULL;
obj->count=0;
}
/**
* Your MinStack struct will be instantiated and called as such:
* MinStack* obj = minStackCreate();
* minStackPush(obj, x);
* minStackPop(obj);
* int param_3 = minStackTop(obj);
* int param_4 = minStackMin(obj);
* minStackFree(obj);
*/