链接: 739. 每日温度
链接: 496.下一个更大元素 I
739. 每日温度
单调栈入门题
这题的关键时保证了栈内所有的元素都是单调递增的(单调栈)
class Solution {
public int[] dailyTemperatures(int[] temperatures) {
Deque<Integer> stack = new LinkedList<>();
int[] res = new int[temperatures.length];
stack.push(0);
for(int i = 1; i < temperatures.length; i++){
if(temperatures[i] <= temperatures[stack.peek()]){ // 当遍历的温度小于等于栈顶元素时则加入栈中
stack.push(i);
}else{
while(!stack.isEmpty() && temperatures[i] > temperatures[stack.peek()]){ // 当遍历的温度大于栈顶元素且栈不为空时则记录结果并将结果弹出
res[stack.peek()] = i - stack.peek();
stack.pop();
}
stack.push(i); // 当栈顶元素大于遍历的温度时则加入栈
}
}
return res;
}
}
496.下一个更大元素 I
class Solution {
public int[] nextGreaterElement(int[] nums1, int[] nums2) {
HashMap<Integer, Integer> map = new HashMap<>();
Deque<Integer> stack = new LinkedList<>();
stack.push(0);
int[] res = new int[nums1.length];
Arrays.fill(res, -1);
for(int i = 0; i<nums1.length; i++){
map.put(nums1[i], i);
}
for(int i = 1; i < nums2.length; i++){
while(!stack.isEmpty() && nums2[i] > nums2[stack.peek()]){
if(map.containsKey(nums2[stack.peek()])){
int index = map.get(nums2[stack.peek()]);
res[index] = nums2[i];
}
stack.pop();
}
stack.push(i);
}
return res;
}
}